1. Field of the Invention
The invention pertains to a hydrodynamic clutch device including a housing which can be brought into working connection with a drive; a hydrodynamic circuit formed by a pump wheel and a turbine wheel; a torsional vibration damper having a drive side transmission element, a takeoff side transmission element, and at least one energy storage group between the transmission elements; and a bridging clutch connecting the housing to the drive side transmission element of the torsional vibration damper.
2. Description of the Related Art
A hydrodynamic clutch device of this type is known from, for example, DE 10 2004 029 157 A1. The hydrodynamic clutch arrangement has a hydrodynamic circuit, formed by a pump wheel, a turbine wheel, and a stator, and is realized as a torque converter, which is designed with a bridging clutch, the piston of which is able to move a plurality of friction elements into and out of engagement with each other. First friction elements are mounted nonrotatably on a housing of the hydrodynamic clutch device, so that this housing, which is connected for rotation in common with a drive, such as the crankshaft of an internal combustion engine, acts as a drive-side friction element carrier. Second friction elements are mounted nonrotatably on a drive-side transmission element of a torsional vibration damper, which thus acts as a takeoff-side friction element carrier. The bridging clutch has friction surfaces located between adjacent friction element carriers. The drive-side transmission element of the torsional vibration damper cooperates with an energy-storage group and a takeoff-side transmission element of the torsional vibration damper to form a damping device, which is connected nonrotatably to a takeoff such as a gearbox input shaft. The energy-storage group is supported in openings in cover plates, which are connected nonrotatably to the takeoff-side friction element carrier, and is also supported in openings provided in the takeoff-side transmission element.
In the known hydrodynamic clutch device, the openings for the energy-storage group in the cover plates and in the takeoff-side transmission element are permeable to the fluid medium present in the housing. Because of these openings, there is the problem that a not inconsiderable portion of the fluid medium moving from a flow inlet to a flow outlet flows through the openings, thus bypassing the friction surfaces of the bridging clutch. Especially during phases in which the friction elements are heated because of slippage, it is possible that this phenomenon can cause a deficiency of cooling fluid medium in the area of the friction surfaces, so that the heat developed at the friction surfaces cannot be carried away. As a result, the load capacity of these friction elements becomes lower than that of better-cooled friction elements.
This basic problem of the openings for the energy-storage group is especially relevant when the known hydrodynamic clutch device is designed as a three-line system. In a three-line system, a pressure space located axially between the drive-side cover of the clutch device and a piston of the bridging clutch is not only sealed off against the hydrodynamic circuit, but also connected to an additional pressure line of a hydraulic system, which means that the hydrodynamic circuit has both a flow inlet and a flow outlet.
A two-line system such as that known from U.S. Pat. No. 7,073,646 is therefore superior with respect to the dissipation of heat from the area of the friction surfaces. In a two-line system, the pressure space located between the drive-side cover of the clutch device and the piston of the bridging clutch is connected to a control line of a hydraulic system, which acts either as a flow inlet or as a flow outlet for fluid medium in correspondence with the operating state of the clutch device at the moment in question, i.e., depending on whether the bridging clutch is open or closed. Because otherwise there is only one other flow inlet or outlet for the hydrodynamic circuit, the fluid medium is forced, as it enters the hydrodynamic circuit or leaves it, to flow across the friction surfaces of the bridging clutch, because the bridging clutch in a two-line system acts as a separation point between the hydrodynamic circuit and the pressure space. For this reason, the use of a torsional vibration damper in a two-line system such as that according to U.S. Pat. No. 7,073,646 does not present a problem, even though this damper has two radially offset damping devices, in which openings which allow the flow of the fluid medium are provided in the cover plates and hub disks to accommodate the drive-side energy-storage group of the drive-side damping device and the takeoff-side energy-storage group of the takeoff-side side damping device. The two energy-storage groups are connected to each other by an intermediate transmission element.
To return to the hydrodynamic clutch devices with the more problematic three-line system: FIG. 1 of U.S. Pat. No. 6,244,401 shows a design in which a clutch device operating according to this system cooperates with a torsional vibration damper with two damping devices, each with openings which promote the flow of the medium. Because this design is especially critical with respect to the overheating of the friction elements of the bridging clutch as explained above, FIG. 2 of the '401 patent shows a torsional vibration damper in which a closed cover plate is assigned to the radially outer damping device. A cover plate of this type, however, takes up more space in the axial direction than a cover plate with openings for the energy-storage group, and this extra space is located precisely in the area of the torsional vibration damper where it has already been made larger in the axial direction because of the presence of an energy-storage group. Presumably for this reason, the torsional vibration damper according to the '401 patent does not have a closed cover plate for the radially inner damping device.